Dielectric relaxation studies on the submicron crystalline La2Mo2O9 oxide-ion conductors

Submicron crystalline La2Mo2O9 bulk samples with grain size of about 0.3 mum were successfully synthesized by sol-gel method and sintering process assisted by phase transformation. In the dielectric measurement, two prominent relaxation peaks with almost the same height (P-d1 at lower-temperature and P-d2 at higher-temperature) are observed in temperature spectrum as well as in frequency spectrum, which are associated with the short-distance diffusion of oxygen vacancies. The activation energies and relaxation times At infinite temperature of these two peaks are deduced as (1.22 ev, 3.3 x 10(-16) s) and (1.35 eV, 5.9 X 10(-16) s), respectively. The DC conductivity of the submicron crystalline samples, which is about 0.02 S/cm. when extrapolated to 800degreesC, is much smaller than that of the macrocrystalline samples. The reciprocal of the peak height for P-d1 peak is linearly proportional to temperature, while that for P-d2 peak is temperature independent. The reason for the co-appearance and the possible relaxation dynamics of the two peaks are discussed. (C) 2003 Elsevier Science B.V. All rights reserved.